Physics3D/RigidBody3D: Fix movement of already moved instance

src/Nazara/Physics3D/RigidBody3D.cpp

@@ -70,6 +70,7 @@ namespace Nz
 	m_gravityFactor(object.m_gravityFactor),
 	m_mass(object.m_mass)
 	{
+		if (m_body)
 			NewtonBodySetUserData(m_body, this);
 	}
 
@@ -411,7 +412,9 @@ namespace Nz
 		m_torqueAccumulator  = std::move(object.m_torqueAccumulator);
 		m_world              = object.m_world;
 
+		if (m_body)
 			NewtonBodySetUserData(m_body, this);
+
 		return *this;
 	}